WordPress | Function | Featured image or SVG

feat_img_or_svg.php

<?php  
// If the post does not have a featured image 
function feat_img_fallback($image_size, $post_id, $alt) {
    if ( has_post_thumbnail($post_id) ) {
        $image_id = get_post_thumbnail_id($post_id);
        $image_src = wp_get_attachment_image_src($image_id, $image_size);
        $image_url = $image_src[0];
        $image = '<img src="' . $image_url . '" alt="' . $alt . '">';
    } else {
        $image_width = $image_size . '_size_w';
        $image_width = get_option($image_width);
        $image_height = $image_size . '_size_h';
        $image_height = get_option($image_height);
        $image = '<svg xmlns="http://www.w3.org/2000/svg" width="' . $image_width . '" height="' . $image_height . '"><path d="M0 0h' . $image_width . 'v' . $image_height . 'H0z"/></svg>';
    }
    return $image;
}
?>

Featured image or inline SVG

In short you pass in the size you need (standard WP sizes), the post ID and the desired alt tag.

The function then checks for a featured image, if it's available it returns the relevant image.

If there's no attached image, the function grabs the sizing of the desired image size and creates and returns an inline SVG.

There's a variation on this here which returns the URL of the featured image or a placeholder URL.